Quick ReadA retirement account's beneficiary form legally overrides any will, so an outdated 1990s form can send hundreds of thousands of dollars through costly probate. Rollovers to new custodians often reset beneficiary designations to the estate default, a pitfall most account holders never notice. Under the SECURE Act, an account passing through an estate instead of a named beneficiary can shrink the distribution window from 10 years to 5, costing six figures in taxes. Under federal rules, a beneficiary designation on a 401(k) or IRA controls the account, regardless of what a later will says. When the named person has died, cannot be located, or was removed from the family through divorce, the account can default to the estate and land in probate.